The present invention relates to an ink jet recording apparatus including an ejection head for ejecting ink. More specifically, the present invention relates to an ink jet recording apparatus including a cleaning system for cleaning an ejection head.
There has been known an electrostatic ink jet recording apparatus in which ink obtained by dispersing fine particles containing colorants in a carrier liquid is ejected as ink droplets through exertion of electrostatic forces onto the ink, to thereby perform drawing (image recording). In addition, as one type of the electrostatic ink jet recording apparatus, there has also been known an electrostatic concentrated ink jet recording apparatus which uses ink obtained by dispersing charged particles containing colorants in a carrier liquid, causes the colorant particles to move to ejection portions (nozzles) through migration by means of electrostatic forces or the like, and ejects ink droplets under a state where the ink is concentrated.
In the electrostatic ink jet recording apparatus, ordinarily, the ink is circulated through a predetermined ink circulation system including a main ink tank (main tank) for reserving the ink and an ejection head, to thereby supply the ink to the ejection head to perform drawing.
In an ink jet recording apparatus in which ink is circulated and is supplied to an ejection head, which is not limited to the above-mentioned electrostatic ink jet recording apparatus, when the apparatus is left under a state where the ink circulation is stopped and the ink (the carrier liquid) is evaporated, there may occur a problem in that the ink is dried in ejection ports (nozzles) and in the ink circulation system to adhere thereto, which leads to clogging, a circulation failure, or the like.
In order to solve the problem inherent to the ink jet recording apparatus, various techniques are proposed.
In JP 2002-1989 A, for instance, there is disclosed an ink jet printer including an ink circulation system and a cleaning liquid circulation system, in which a three-way solenoid valve is provided on an ejection nozzle side to alternately supply ink and a cleaning liquid, and a three-way solenoid valve is provided on a side for capturing unnecessary particles with a gutter to separately recover the ink and the cleaning liquid, where a cleaning-side solenoid of the three-way solenoid valve on the recovery side is delayed to drive upon a switching instruction to the three-way solenoid valve on the supply side to thereby prevent a cleaning waste liquid from being mixed into an ink tank.
Also, JP 3286209 B discloses an ink jet recording apparatus that leads ink and a solvent held in an ink container and a solvent container provided in an apparatus main body into a print head through an ink jet tube and a solvent tube respectively, and performs printing and cleaning by selectively supplying the ink and the solvent to each nozzle using a control valve provided in the print head, where an ink chamber located inside an ink jet port of the nozzle is connected to an ink container in the apparatus main body through a circulation tube to form a circulation passage, and the solvent is supplied to the ink chamber of the nozzle by operating the control valve for cleaning, to let a part of the solvent in the ink chamber flow through the circulation path by causing the ink in the ink chamber to jet from the ink jet port.
Here, with consideration given to contamination of the ink, the dispersion medium of the ink has conventionally been used as the cleaning liquid for the cleaning. However, a solvent used in the dispersion medium has a high intrinsic resistance value, which causes an insulating material (resin or rubber-made tube) in the circulation path to be charged through friction with the cleaning liquid when the cleaning liquid is circulated. When the circulation path is charged through the cleaning liquid circulation in the manner described above, this leads to a problem in that a charge amount of the ink circulated through the circulation path changes after the cleaning as compared with that before the cleaning.
In particular, in the case of the electrostatic ink jet recording apparatus that performs ink ejection by exerting electrostatic forces onto the ink, the unstable charge amount ink leads to a problem in that the ejection characteristics of the ink jet head fluctuate and image reproducibility is deteriorated.
A method for preventing the circulation path from being charged includes a method in which a conductive tube is used as the piping of the circulation path. However, the cost of the conductive tube is twice as high as that of a Teflon (registered trademark) PFA tube, which leads to a problem in that the cost of the apparatus is inevitably increased.
Alternatively, for preventing the circulation path from being charged, it is also possible to use a method in which metallic piping is adopted for every piping of the circulation path, however, in the case of using a head of head scanning type or the like, or in a case where the circulation path is not fixed, the piping needs to be flexible and therefore it is impossible to use the metallic piping.